Barium sulfate (BaSO4), a white or yellowish odourless powder, is the barium salt of sulfuric acid. The name comes from the Greek word for heavy = barys, which indicates the element’s high atomic weight. It is very insoluble in water but soluble in concentrated sulphuric acid, forming an acid sulphate dilution. Due to its extremely low water solubility, barium sulfate, as compared to other barium compounds, is non-toxic.
The mineral Barite, which is composed largely of barium sulphate, is a common ore of barium. Barium has a green color in a flame test which is used to separate barite from other minerals. Stones made from impure barium sulphate, the natural impurities, can be ferric oxide or silicon dioxide for example, and glow when exposed to light, the phenomenon is called phosphorescence.
In nature, barium sulfate is found as crystals which due to their high density are referred to as barite (heavy spar). Considerably larger deposits are found in China which, in addition, ranks first in barium sulfate mining. The naturally occurring type of barium sulfate is used most commonly. For applications that require very pure white colors, barium sulfate is obtained by precipitation as “blanc-fixe” (permanent white).
Barium sulphate is used as fillers for plastics, paint, rubber and resins. It increases the plasticity and weight of plastic materials that are used for sound insulation in e.g., car mats, carpet coatings, or plastic sewage pipes. The chemical inertness and high temperature stability of barium sulfate are made use of in friction linings.
It can also be found in photographic papers and is used as a pigment. Together with zinc oxide it is known as a white pigment called Lithophone and another white pigment is called Blanc fixe. Blanc fixe has except barium sulphate also sodium sulphate as a component, but pure precipitated barium sulphate is also called Blanc fixe.
Barium sulphate precipitated improves the volume and consistency, viscosity and workability of e.g., fillers, surfacers, and primers. Blanc-fixe is added for easy glazing of glossy papers and photographic papers (barite papers). Burning of such papers leaves whitish barium sulfate deposits. In the textile industry, barium sulfate is found as a finish for linen goods and an agent for rayon matting during etching and printing.
Due to its high coefficient of absorption for gamma radiation and X-radiation, barium sulfate is used in concrete (barite concrete, barite cement) that screens nuclear reactors. It is contained, in addition, in numerous radio-opaque substances (radio-opaque barite).